///////////////////////////////////////////////////////////////////////////
//                   __                _      _   ________               //
//                  / /   ____  ____ _(_)____/ | / / ____/               //
//                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
//                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
//               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
//                           /____/                                      //
//                                                                       //
//               The Next Generation Logic Library                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright 2015-20xx Christoph Zengler                                //
//                                                                       //
//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
//  You may obtain a copy of the License at                              //
//                                                                       //
//  http://www.apache.org/licenses/LICENSE-2.0                           //
//                                                                       //
//  Unless required by applicable law or agreed to in writing, software  //
//  distributed under the License is distributed on an "AS IS" BASIS,    //
//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
//  implied.  See the License for the specific language governing        //
//  permissions and limitations under the License.                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////

/******************************************************************************************
 * MiniSat -- Copyright (c) 2003-2006, Niklas Een, Niklas Sorensson
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and
 * associated documentation files (the "Software"), to deal in the Software without restriction,
 * including without limitation the rights to use, copy, modify, merge, publish, distribute,
 * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * The above copyright notice and this permission notice shall be included in all copies or
 * substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT
 * NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
 * OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ******************************************************************************************/

package org.logicng.solvers.datastructures;

import org.logicng.collections.LNGIntVector;
import org.logicng.solvers.sat.MiniSatStyleSolver;

/**
 * A minimalistic heap implementation.
 * @version 1.3
 * @since 1.0
 */
public final class LNGHeap {

  private final MiniSatStyleSolver s;
  private final LNGIntVector heap;
  private final LNGIntVector indices;

  /**
   * Constructs a new heap for a given solver.  The solver is required to access it's activity information stored
   * for variables.  The initial size of the heap is 1000 elements.
   * @param solver the solver
   */
  public LNGHeap(final MiniSatStyleSolver solver) {
    this.s = solver;
    this.heap = new LNGIntVector(1000);
    this.indices = new LNGIntVector(1000);
  }

  /**
   * Returns the left position on the heap for a given position.
   * @param pos the position
   * @return the left position
   */
  private static int left(int pos) {
    return pos * 2 + 1;
  }

  /**
   * Returns the right position on the heap for a given position.
   * @param pos the position
   * @return the right position
   */
  private static int right(int pos) {
    return (pos + 1) * 2;
  }

  /**
   * Returns the parent position on the heap for a given position.
   * @param pos the position
   * @return the parent position
   */
  private static int parent(int pos) {
    return (pos - 1) >> 1;
  }

  /**
   * Returns the size of the heap.
   * @return the size of the heap
   */
  public int size() {
    return this.heap.size();
  }

  /**
   * Returns {@code true} if the heap ist empty, {@code false} otherwise.
   * @return {@code true} if the heap ist empty
   */
  public boolean empty() {
    return this.heap.size() == 0;
  }

  /**
   * Returns {@code true} if a given element is in the heap, {@code false} otherwise.
   * @param n the element
   * @return {@code true} if a given variable index is in the heap
   */
  public boolean inHeap(int n) {
    return n < this.indices.size() && this.indices.get(n) >= 0;
  }

  /**
   * Returns the element at a given position in the heap.
   * @param index the position
   * @return the element at the position
   */
  public int get(int index) {
    assert index < this.heap.size();
    return this.heap.get(index);
  }

  /**
   * Decrease an element's position in the heap
   * @param n the element
   */
  public void decrease(int n) {
    assert this.inHeap(n);
    this.percolateUp(this.indices.get(n));
  }

  /**
   * Inserts a given element in the heap.
   * @param n the element
   */
  public void insert(int n) {
    this.indices.growTo(n + 1, -1);
    assert !this.inHeap(n);
    this.indices.set(n, this.heap.size());
    this.heap.push(n);
    this.percolateUp(this.indices.get(n));
  }

  /**
   * Removes the minimal element of the heap.
   * @return the minimal element of the heap
   */
  public int removeMin() {
    int x = this.heap.get(0);
    this.heap.set(0, this.heap.back());
    this.indices.set(this.heap.get(0), 0);
    this.indices.set(x, -1);
    this.heap.pop();
    if (this.heap.size() > 1)
      this.percolateDown(0);
    return x;
  }

  /**
   * Removes a given element of the heap.
   * @param n the element
   */
  public void remove(int n) {
    assert this.inHeap(n);
    int kPos = this.indices.get(n);
    this.indices.set(n, -1);
    if (kPos < this.heap.size() - 1) {
      this.heap.set(kPos, this.heap.back());
      this.indices.set(this.heap.get(kPos), kPos);
      this.heap.pop();
      this.percolateDown(kPos);
    } else
      this.heap.pop();
  }

  /**
   * Rebuilds the heap from a given vector of elements.
   * @param ns the vector of elements
   */
  public void build(final LNGIntVector ns) {
    for (int i = 0; i < this.heap.size(); i++)
      this.indices.set(this.heap.get(i), -1);
    this.heap.clear();
    for (int i = 0; i < ns.size(); i++) {
      this.indices.set(ns.get(i), i);
      this.heap.push(ns.get(i));
    }
    for (int i = this.heap.size() / 2 - 1; i >= 0; i--)
      this.percolateDown(i);
  }

  /**
   * Clears the heap.
   */
  public void clear() {
    for (int i = 0; i < this.heap.size(); i++)
      this.indices.set(this.heap.get(i), -1);
    this.heap.clear();
  }

  /**
   * Bubbles a element at a given position up.
   * @param pos the position
   */
  private void percolateUp(int pos) {
    int x = this.heap.get(pos);
    int p = parent(pos);
    int j = pos;
    while (j != 0 && this.s.lt(x, this.heap.get(p))) {
      this.heap.set(j, this.heap.get(p));
      this.indices.set(this.heap.get(p), j);
      j = p;
      p = parent(p);
    }
    this.heap.set(j, x);
    this.indices.set(x, j);
  }

  /**
   * Bubbles a element at a given position down.
   * @param pos the position
   */
  private void percolateDown(int pos) {
    int p = pos;
    int y = this.heap.get(p);
    while (left(p) < this.heap.size()) {
      int child = right(p) < this.heap.size() && this.s.lt(this.heap.get(right(p)), this.heap.get(left(p))) ? right(p) : left(p);
      if (!this.s.lt(this.heap.get(child), y))
        break;
      this.heap.set(p, this.heap.get(child));
      this.indices.set(this.heap.get(p), p);
      p = child;
    }
    this.heap.set(p, y);
    this.indices.set(y, p);
  }

  @Override
  public String toString() {
    final StringBuilder sb = new StringBuilder("LNGHeap{");
    for (int i = 0; i < this.heap.size(); i++) {
      sb.append("[").append(this.heap.get(i)).append(", ");
      sb.append(this.indices.get(i)).append("]");
      if (i != this.heap.size() - 1)
        sb.append(", ");
    }
    sb.append("}");
    return sb.toString();
  }
}
